Field of the Invention
The present invention relates to a display apparatus and a control method thereof.
Description of the Related Art
Some examples of color image display apparatuses include a color liquid crystal panel having a color filter, and a light source device (backlight device) which illuminates the back surface of the color liquid crystal panel with white light. Conventionally, as the light source of a light source device, a fluorescent lamp such as Cold Cathode Fluorescent Lamp (CCFL) has been used mainly. However, recent years have seen an increased use of a light emitting diode (LED), which is excellent in terms of power consumption, lifetime, color reproducibility, and environmental load, as the light source of a light source device.
In general, a light source device (LED backlight device) using an LED as a light source has a large number of LEDs. Japanese Patent Application Laid-open No. 2001-142409 discloses an LED backlight device including a plurality of light emitting units each having one or more LEDs. Japanese Patent Application Laid-open No. 2001-142409 also discloses individual control of the brightness of each of the light emitting units. By reducing the emission brightness of the light emitting unit which illuminates with light the region of the screen of a color image display apparatus where a dark image is displayed, power consumption is reduced and the contrast of the image is improved. Such brightness control performed individually for each of the light emitting units in accordance with the characteristic feature of the image is referred to as local dimming control.
On the other hand, when a bright image and a dark image are adjacent to each other in the local dimming control, unevenness referred to as a halo presents a problem. Since the light emitting unit which illuminates with light the region where the bright image is displayed has a high emission brightness, the light from the light emitting unit leaks out into the adjacent region where the dark image is displayed to be visually recognized as unevenness.
To reduce such unevenness, the following method is used. In the method, an emission brightness distribution when each of the light emitting units is individually turned on is obtained in advance. The respective brightnesses of the individual light emitting units that have been determined by local dimming control are subjected to multiplication to be summed up on each other. Thus, the brightness distribution of the light incident on a color liquid crystal panel is determined and, in accordance therewith, the light transmittance of the color liquid crystal panel is adjusted. Japanese Patent Application Laid-open No. 2009-139470 shows an example thereof.